The present invention relates to a ratchet drive mechanism for a screwdriver bit or other work tool.
There are a wide variety of known designs for ratchet tools. Typically, such tools have two modes of operation, either one of which may be selectively set by the user. In the first mode (for example to tighten a screw) ratcheting operation is enabled in a clockwise direction. In the second mode (for example to loosen a screw) ratcheting operation is enabled in an anti-clockwise direction.
However, disadvantageously, many of such tools typically have no third or non-ratcheting mode of operation or setting where ratcheting behaviour can be locked out/disabled and the drive mechanism of the tool engages whether the tool is turned clockwise or anti-clockwise. The advantage of such a third mode can arise, for example, when a user wants to make minor adjustments to the tightness of a screw or to slightly loosen then retighten a screw. In this situation, it can be quite inconvenient to have to switch back and forth between clockwise and anti-clockwise modes of ratcheting operation.
There are at least some ratcheting tools which offer a non-ratcheting mode of operation. An example is that described in U.S. Pat. No. 6,305,248 (Rowlay) granted on Oct. 23, 2001. In this patent, one stated object is to provide a ratchet mechanism which is of short length. It appears to be suggested that this object is compromised by conventional drive mechanisms where pawls extend in the axial direction of a shaft. This is agreed. But, the alternative mechanism suggested by Rowlay appears to be a rather complicated pawl rocking mechanism. Further, the Rowlay mechanism does not appear to combine the objective of short length with strength and long term durability.
Those relatively few tools which do offer a non-ratcheting mode of operation, are considered relatively complex in structure or operation. Further, they are not considered well adapted for smooth ratcheting operation under high torque loads or to resist side forces or impacts on the drive shaft of the ratchet drive mechanism or on a screwdriver bit or other work tool carried by the drive shaft.